Method for heat insulating a rotational casting mold

ABSTRACT

A process for insulating a rotational casting mold for use in a casting process for making a substantially even thickness fascia. The fascia is prepared by placement of a plastic powdered material into an enclosed mold, heating and agitating the mold for distributing the plastic powder on the mold surfaces to provide a substantially even thickness fascia part on the molding surface. The mold includes first mold surfaces for defining critical portions of the mold which correspond to the desired portions of the mold for forming the finished shape of the part by melting of the plastic powder to a uniform film along the surface. The mold also includes second mold surfaces defining non-critical portions of the mold where it is undesirable for plastic filming to occur. An insulating material covers the second mold surfaces, creating a temperature barrier on the second mold surfaces reducing the effective temperature of the second mold surfaces such that the plastic powder will melt on the first mold surfaces but not on the second surfaces. The process for insulating the rotational casting mold includes cutting a plurality of sections of insulating material to fit the non-critical portions of the mold, coating the non-critical portions of the mold with a heat resistant bonding material before assembling the cut sections onto the non-critical portions followed by curing of the bonding material.

TECHNICAL FIELD

The present invention relates to an improved rotational casting mold ofthe type used for producing fascia type parts.

BACKGROUND

Rotational casting is a method of producing fascia type parts or otherparts which require a thin skin type portion. For instance, therotational casting process is used to produce instrument panel fasciasin the automotive industry, but is also useful whenever a fascia typepart which has a skin type layer having an even thickness and acontoured surface is desired to be produced.

Generally a rotational cast process consists of the use of a mold havingan inner cavity which cavity has molding surfaces which are contoured tocorrespond to that of a finished part. Commonly the mold is configuredin two halves each of which has a molding surface for a separate fasciapart. Plastic power molding material corresponding to the desiredmaterial used in the final part is introduced into the cavity formed bythe two halves of the mold. The mold is then placed into an oven andthen heated to a temperature which will induce flashing or melting onthe molding surfaces in the plastic material used. To ensure an eventhickness the mold is agitated or rotated to evenly distribute theplastic powder along the entire mold surfaces. Thus, as the plasticpowder touches the heated mold surfaces it instantly flashes or meltsand creates a uniform coating over the mold surfaces which is insured bythe rotation and/or agitation of the mold. Subsequently the mold isallowed to cool and it then must be removed from the assembly, trimmedto its proper dimensions and may then be used.

Due to the nature of this process in that the two halves must be joinedtogether and sealed so that the powder will not escape and will bedistributed throughout the surfaces during the rotating and agitatingprocess, the mold cavities are generally produced with extraneous ornon-critical areas which are there to provide a joining of the two moldsin the cavity or for other reasons other than to provide a moldingsurface for the final part. These extraneous or non-critical surfaceswhile necessary to the molding process create extra surfaces which causeunwanted flashing material in the finished product in that they are alsoheated during the casting process and subsequently powdered materialcoats these surfaces along with the critical molding surfaces. Thiscreates undesirable extra material in the finished part which must beremoved or trimmed from the part prior to installing the part or usingthe part in its finished form.

Thus, while the finished part obtained from this process creates asuitable part the process necessitates the step of trimming the part toremove the excess material which is somewhat time consuming and alsocreates extra material usage because of the wasted material which mustbe trimmed before shipping or using the final part. These extra stepsare undesirable in that excess labor and product costs are consumed bysuch a procedure. Therefore, it is desirable to solve this problem ofwasted labor and material in the rotational casting art to provide costsavings in production and also an improved finished product.

SUMMARY OF THE INVENTION

Therefore, according to the present invention there is provided a moldfor a casting process wherein it is desirable to make a substantiallyeven thickness fascia through placement of a plastic powder materialinto an enclosed mold in creating the part by heating and rotating themold for distributing the powder for substantially evenly covering thesurface of the mold. The present invention includes a first mold surfaceon the mold for defining critical portions of the mold which correspondto the desired portions for forming the finished part by melting anddistribution of plastic powder for forming the plastic part. Second moldsurfaces are provided on the mold, which include the non-criticalportions of the mold wherein it is undesirable for such plastic filmingto occur. An insulating material is attached to the second mold surface.The insulating material is for creating a temperature barrier on thesecond mold surfaces for reducing the effective temperature of thesecond mold surfaces whereby plastic powder will melt and form theuniform coating on the first surface and will not melt on the secondsurface.

Also provided in the present invention is a method for shielding a moldused in a rotational casting process whereby fascia parts having asubstantially even surface are manufactured. The method includes cuttinga plurality of sections from an insulating material. The sectionscorrespond to discrete portions of the non-critical surfaces of saidmold and are for assembly onto the non-critical surfaces. Thenon-critical surfaces are coated with a layer of heat resistant bondingmaterial. The sections are then assembled onto their correspondinglocations onto the surfaces of the mold and the assembly is allowed tocure, thereby providing the mold of the present invention.

It is therefore an object of the present invention to provide a moldingassembly which will produce a finished part with reduced labor and lesswasted material.

It is a further object of the present invention to provide a mold foruse in a rotational casting process which will substantially reduce theamount of wasted material normally incident with such a process.

DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdescription when considered in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a perspective view of a typical molding assembly in which thepresent invention may be useful;

FIG. 2 is a perspective view showing the laying out of sectionscorresponding to the non-critical portions of the mold on an insulatingmaterial;

FIG. 3 is a perspective view showing the cutting out of sections fromthe insulating material for insulating in the mold of the presentinvention;

FIG. 4 is a perspective view showing the application of bonding materialin the present invention;

FIG. 5 is a perspective view showing the assembling of the insulatingmaterial into the mold of the present invention;

FIG. 6 is a perspective view showing the process of sealing the seamsfor producing the mold of the present invention;

FIG. 7 is a perspective view showing the preparation of the moldingassembly for molding the fascia part;

FIG. 8 is a perspective view showing the rotational molding apparatusbeing agitated for molding of a part by the method of the presentinvention;

FIG. 9 is a perspective view showing the removal of the finished part.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 there is shown a rotational mold in which theinvention may be used. Mold 10 includes critical surface portions 12 andnon-critical portions 14. The critical portions 12 are those portions ofthe mold which define the shape of the final produce which is desired.The non-critical portions 14 are those portions of the mold which do notprovide any molding surfaces for the final part and which are extraneousto the molding of the final part. These non-critical surfaces mayinclude flashing areas and other areas which may be useful in mating ofthe two halves of the mold together or for other purposes which areextraneous of the use in producing the actual shapes of the finishedpart. Thus, the non-critical areas include any surfaces of the cavity ofthe mold wherein it is undesirable or unwanted for plastic flashing orcoating to occur.

As shown in FIG. 2, these non-critical surfaces 14 are laid out on ainsulating sheeting material 16 so that the sheeting material may be cutinto sections 18 which correspond to respective parts on the mold 10which correspond to surfaces in the non-critical section of the mold.

In FIG. 3 these sections are then cut out of the insulating material toprovide for assembly onto the non-critical portions of the mold later inthe present process. The insulating material may be of many types whichwill insulate the non-critical molding surfaces from heat build up whichwould cause plastic material to flash thereon and cover these surfaces.Preferably a phenolic sheeting material is used such as that generallyused in circuit boards, however, any other insulating materials could beused which would insulate the non-critical molding surfaces such thatplastic powder will not melt when coming into contact with theinsulating material when used in the rotational casting process. In thepreferred embodiment of the present invention a phenolic boardNEMAgrade-3 is used which is about 0.250 inches thick.

As shown in FIG. 4 a silicone caulking material 20 is used and appliedin a coating to all non-critical surfaces of the mold installation wherethe insulating sections are to be installed. Preferably the materialused is a RTV silicone which is designated by GE102. However, othermaterials could be used which will withstand repeated heat and coolcycles and retain the adhesiveness. The silicone layer 22 is applied inan approximately 1/8 inch thick coating over the non-critical surfacesof the mold. The silicone material provides a bonding for theinstallation of the phenolic sheeting and also insulates the assemblyfurther from heat transfers from the non-critical mold surfaces.

In FIG. 5 the sections which were cut out from the phenolic sheeting arethen fitted into the respective places in the mold. As shown in FIG. 6,after the mold is allowed to dry partially such that the pieces are heldinto place, the installer will caulk all exposed edges and jointsbetween the sections for providing an integration between the sectionsand further preventing any plastic from seeping between the phenolicboard and the mold surfaces which would cause undesirable flashing ofthe plastic material.

At this point in time the individual sections may be further fastenedonto the mold surface to provide a permanent installation. Thisfastening may be done by countersinking bolts 24 into the phenolicassembly. Bolts or screws 24 are then inserted through the phenolicsections 18 and into the mold to hold the phenolic sections 18 on themold surfaces. Phenolic caps may then be fabricated to fill in voidsleft or cover exposed portions of the bolts after countersinking thesebolts, by first inserting some silicone caulking material into thecounter sunk holes and thereafter capping the holes with a phenolicplug. Alternatively, other insulating materials such as siliconeadhesive may be used to insulate the exposed portions of the bolts orscrews 24. This provides a further permanency to holde the siliconeadhered phenolic board onto the non-critical molding surfaces of therotational casting mold, alternatively, the phenolic sections may besecured with bolts or fasteners alone. Upon completion of this step themolding tool has the phenolic assembled. The installer must thereafterinspect all joints in the perimeter of the phenolic to ensure a goodseal. The assembly must then be allowed to cure for approximately 48hours in order to allow complete curing of the silicoine caulkingmaterial which will further extend the life of the mold.

Thus, provided in the present invention is an improved casting mold inwhich the non-critical areas of the mold have been insulated by thephenolic sheeting process such that the surface temperature of thephenolic sheeting will not rise to a high enough temperature during theheating and agitation process to cause plastic powder which comes incontact with the critical surfaces to melt thereon. Thus, when the moldis placed into the oven and rotationally agitated the powder selectivelymelts onto the critical molding surfaces for forming the part but doesnot run off onto extraneous non-critical areas in the mold which areshielded by the phenolic. It is estimated that this will result in a 20to 40 percent decrease in run off and therefore a resultant decrease inactual material used. Furthermore, this results in less man hour time incompleting the molding of the part since the part requires less trimmingor no trimming by using the method of the present invention.

As shown in FIG. 7 a powdered plastic material 26 is then placed in arelease cylinder 28 in the molding apparatus. The halves are then closedonto one another. The molds are placed in the rotational agitatingapparatus and are heated and agitated for forming a part 30 as shown inFIG. 8. The rotational apparatus is moved to a large oven wherein themold surfaces are heated from the outside. The assembly is rotated andagitated to provide for distribution of the plastic. This heatingprocess will heat the critical surface areas to a flashing temperatureof the plastic and when the plastic powder touches the critical surfacesareas it will melt and form a film thereon which becomes the final part.In the present invention the phenolic insulation material will lower thetemperature of the phenolic surface contacting the plastic powder belowthe flashing temperature of the plastic thereby eliminating wastedmaterial since the plastic will not flash on these surfaces. Uponcompletion of this rotational agitation the molding apparatus is therebycooled, the halves are opened and the part 30 may then be removed asshown in FIG. 9. Thus, the present invention provides a part which issubstantially free from excess wasted material and may be removed andsent directly to an area for further processing or shipping out. Thus,the mold can be prepared in the manner described above and reused forfurther molding. It has been found that such a construction willwithstand normal chemical cleaning processes used to clean these molds.

The invention has been described in an illustrative manner and it is tobe understood that the terminology which has been used is intended to bedescriptive rather than limitative. Obviously, many modifications andvariations of the invention are possible in light of the aboveteachings. Therefore, it is to be understood that within the scope ofthe amended claims the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. A method for shielding a mold having first andsecond mold surfaces respectively defining critical and non-criticalportions of said mold, said mold being for use in a rotational castingprocess whereby a fascia part having a substantially even thickness isproduced, said method comprising the steps of:(a) cutting a plurality ofsections from heat insulating material, said sections corresponding todiscreet portions of said second mold surfaces defining saidnon-critical portions of said mold for assembly onto said non-criticalportions; (b) coating said second surfaces with a layer of heatresistant bonding material; (c) then assembling said plurality ofsections onto their corresponding locations on said second surfaces ofsaid mold; and (d) allowing the heat resistant bonding material to curethereby bonding said sections onto said second mold surfaces of saidmold whereby the sections insulate the non-critical portions of the moldto provide a temperature barrier on the non-critical portions such thatthese non-critical portions remain below the melting point temperatureof a preselected plastic material to prevent melting of plastic on saidnon-critical portions.
 2. The method according to claim 1 wherein saidsections of step (a) are taken from a phenolic board material.
 3. Themethod according to claim 1 wherein said heat resistant bonding materialis a silicone adhesive material.
 4. The method according to claim 1wherein said sections are also secured to said mold by a fastening meansupon completion of step (d).
 5. The method according to claim 4 whereinsaid fastening means further comprises a bolt which is counter sunk intosaid heat insulating material and attached to said mold for securingsaid sections to said non-critical portions of said mold.
 6. The methodaccording to claim 5 wherein portions of said countersunk bolts arecovered with an insulating material.
 7. The method of claim 6 whereinsaid insulating material is a silicone adhesive, a phenolic cap or acombination of a silicone adhesive and a phenolic cap.